1. Field of the Invention
This invention relates to a solder ball mounting device for mounting solder balls on a workpiece such as a substrate, and more particularly to an improvement of control means for controlling a pressure and a head position at the time of suction of solder balls in a BGA (ball grid alley) solder ball mounting device.
2. Description of the Related Art
In mounting a plurality of solder balls on a substrate with a solder ball mounting device, in general the following method is employed: A sucking plate having solder ball sucking holes is disposed under the lower surface of a sucking head, and vacuum pressure is utilized to suck solder balls in the sucking holes, and then the solder balls thus sucked are mounted on the substrate. A means has been developed that, in the ball sucking operation, solder balls in a solder ball supply box are caused to float. In order to employ this solder ball floating method to suck solder balls at high speed thereby to shorten the time required for sucking solder balls, it is necessary to increase the degree of vacuum; that is, the solder ball sucking operation is carried out with a large flow rate of solder balls (hereinafter referred to as "a large ball-sucking flow rate", when applicable).
If, in order to increase the solder ball sucking speed, solder balls are sucked with a large ball-sucking flow rate by a high degree of vacuum, and held, then as shown in FIG. 4 air leaks through the contact section of a solder ball 3 and a sucking plate 30. The air leakage sucks an additional solder ball 31. That is, two solder balls are absorbed ("a double ball phenomenon"). The contact surface of the sucking plate 30 and the solder ball 3 is not completely circular, and the solder balls 3 is not completely spherical, as a result of which a gap is formed therein. Through this gap, a force for sucking another solder ball 31 is formed, so that the double ball phenomenon occurs. If the degree of vacuum of the suction pressure is increased, the force of suction through the gap is increased, so that the frequency of occurrence of the double ball phenomenon is also increased.